A storage system typically comprises one or more storage devices into which information may be entered, and from which information may be obtained, as desired. The storage system includes a storage operating system that functionally organizes the system by, inter alia, invoking storage operations in support of a storage service implemented by the system. The storage system may be implemented in accordance with a variety of storage architectures including, but not limited to, a network-attached storage environment, a storage area network and a disk assembly directly attached to a client or host computer. The storage devices are typically disk drives (or flash-based devices) organized as a disk array, wherein the term “disk” commonly describes a self-contained rotating magnetic media storage device. The term disk in this context is synonymous with hard disk drive (HDD) or direct access storage device (DASD).
The storage operating system of the storage system may implement a high-level module, such as a file system, to logically organize the information stored on volumes as a hierarchical structure of storage objects, such as files and logical units (LUs). A known type of file system is a write-anywhere file system that does not overwrite data on disks. An example of a write-anywhere file system that is configured to operate on a storage system is the Write Anywhere File Layout (WAFL®) file system available from NetApp, Inc. Sunnyvale, Calif.
The storage system may be further configured to allow many servers to access storage objects stored on the storage system. In this model, the server may execute an application, such as a database application, that “connects” to the storage system over a computer network, such as a point-to-point link, shared local area network (LAN), wide area network (WAN), or virtual private network (VPN) implemented over a public network such as the Internet. Each server may request the data services of the storage system by issuing access requests (read/write requests) as file-based and block-based protocol messages (in the form of packets) to the system over the network.
A plurality of storage systems may be interconnected to provide a storage system architecture configured to service many servers. In some embodiments, the storage system architecture provides one or more aggregates, each aggregate comprising a set of one or more storage devices (e.g., disks). Each aggregate may store one or more storage objects, such as one or more volumes. The aggregates may be distributed across a plurality of storage systems interconnected as a cluster. The storage objects (e.g., volumes) may be configured to store content of storage objects, such as files and logical units, served by the cluster in response to multi-protocol data access requests issued by servers.
Each storage system (node) of the cluster may include (i) a storage server (referred to as a “D-blade”) adapted to service a particular aggregate or volume and (ii) a multi-protocol engine (referred to as an “N-blade”) adapted to redirect the data access requests to any storage server of the cluster. In the illustrative embodiment, the storage server of each storage system is embodied as a disk element (D-blade) and the multi-protocol engine is embodied as a network element (N-blade). The N-blade receives a multi-protocol data access request from a client, converts that access request into a cluster fabric (CF) message and redirects the message to an appropriate D-blade of the cluster.
The storage systems of the cluster may be configured to communicate with one another to act collectively to increase performance or to offset any single storage system failure within the cluster. The cluster provides data service to servers by providing access to a shared storage (comprising a set of storage devices). Typically, servers will connect with a storage system of the cluster for data-access sessions with the storage system. During a data-access session with a storage system, a server may submit access requests (read/write requests) that are received and performed by the storage system.
Each storage system may be associated with one or more volumes (e.g., data volumes stored on storage devices). A snapshot operation may be performed to create a read-only copy of the volumes. The snapshot may be utilized by a file system to create a point in time view or image of a consistency group comprising one or more volumes that are stored on one or more storage devices. However, in conventional snapshot operations, incoming write requests to the volumes may be fenced or suspended for a significant period of time. For example, write requests to volumes subject to the snapshot may be suspended until the snapshot operation has finished or until a snapshot operation for a corresponding volume has been finished. As such, write requests for a volume may be fenced or suspended for a significant period of time and such a period of time may result in an application issuing the write requests to time out (due to not being able to execute write requests). Furthermore, the fencing or suspending of write requests to a volume may be dependent on the specifics of the volume and/or application. For example, the amount of time that a volume may be fenced may be dependent upon the data set size of the volume. As such, the fencing or suspension time period may be variable (e.g., not deterministic) as it may vary based on the volume and application.
Thus, an effective method and system for creating a crash-consistent snapshot operation of a consistency group is needed. For example, a system and method for creating a crash-consistent snapshot operation that is scalable and deterministic to address application timeout issues is needed.